Refrigerant-capable heat exchanger made from bendable plastic tubing and method

ABSTRACT

The present invention relates to a plastic tube heat exchanger suitable for refrigerant use is provided by wrapping a layer of tubes around a curved surface, on a base which is generally perpendicular to the surface. Several to many tubes can be in each layer. Then, further layers can be wrapped continuously by overlaying the first layer. Heat exchangers, including refrigerant apparatus, condensers and evaporators, can be made in this configuration. Processes and articles of manufacture are parts of the invention.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under b 35 U.S.C. §119 from U.S.Provisional Application Ser. No. 60/238,507 (filed Oct. 6, 2000), whichis incorporated by reference herein for all purposes as if fully setforth.

BACKGROUND OF THE INVENTION

[0002] Plastic tube heat exchangers are known in the art, however, ithas proven to be difficult to use existing technology to make practicalrefrigerant heat exchangers by the existing techniques.

[0003] Some of the patents disclosing plastic tube heat exchangersinclude U.S. Pat. No. 4,484,624—Vleggaar et al., 1984, and U.S. Pat. No.4,867,233—Gemeinhardt, 1989. The former discloses various ways ofconfiguring tubes inside a heat exchanger, including winding overlappingspirals, and the latter includes ways to gather together the ends of abundle of tubes and connect them to a common header.

[0004] Refrigerant heat exchangers include condensers and evaporators.Typically an evaporator consists of a number of finned metal tubes,typically ¼ inch (6.35 mm) outer diameter with aluminum fins, the tubeshaving a greater internal diameter than the liquid refrigerant inlettubes, to allow for expansion and cooling, and having a specified lengthto allow for complete evaporation to the gaseous phase. There are otherlimitations with metal heat exchangers with fins in other shapes, suchas those wound in the shape of open bee hives, with a fan in the middle.

[0005] Condensers are configured in an analogous manner, but usuallymust operate at higher pressures to effect conversion of the gaseousrefrigerant to a liquid phase. When attempting to design arefrigerant-capable exchanger from plastic tubing, a number of factorsmust be considered:

[0006] a) Refrigerant to air exchangers have a relatively low flow rateof refrigerant inside the tubes. It is therefore possible to designexchangers with fairly long tubes, as limited by pressure dropconsiderations. The use of long tubes allows for a reduction in thenumber of tube connections, for a given exchanger surface area.

[0007] b) The need to handle high pressure further requires that thepolymeric tubing for evaporators and condensers should be small indiameter.

[0008] c) The use of small diameter (1.5 mm OD) further provides a largesurface area for heat transfer, per unit of volume, with the potentialof matching the heat duty of a metal exchanger, its ability to handle acertain amount of heat exchange in a period of time, in a smallervolume.

[0009] By taking these factors into account, it has been determined thatindividual tube lengths of 10-30 ft (3.3-10 m) are suitable for therefrigerant-air exchangers. For practical reasons it is desirable toform tubing of these lengths in some sort of coil, in order to expose alarge surface area to a relatively localized air stream.

[0010] Earlier work on polymeric refrigerant-to-air exchangers involvedcoiling some woven tubing and blowing air through the face of the coilas a replacement for a finned-metal exchanger of rectangular shape. Oneof the drawbacks of this design is that the volume in the center of thecoil, inside the innermost winding, is unavailable for heat transfer andis mainly wasted space. To minimize the wasted space in the center, itis desirable to use tubing with a very small coiling radius to avoidkinking the tubing, and this can impose limitations on the choice ofmaterials or dimensions of the tubing.

BRIEF DESCRIPTION OF THE DRAWING(S)

[0011] FIG. 1 is a plan view of the process of the invention, startingto lay down the tubes.

[0012] FIG. 2 is a perspective schematic view of the process when thefirst layer of tubes has been laid down and the tubes are being elevatedto start the second layer.

[0013] FIG. 3 is a plan view of a plastic tube heat exchanger of theinvention which could be a refrigerant heat exchanger, including acondenser and an evaporator.

[0014] FIG. 4 is an elevation view of a plastic tube heat exchanger ofthe invention, showing what FIG. 3 would look like generally inelevation.

[0015] FIG. 5 is a side view of a spacer used in the invention.

[0016] FIG. 6 is a plan view of the spacer of FIG. 5.

BRIEF SUMMARY OF THE INVENTION

[0017] The present invention provides a plastic tube heat exchangerutilizing for separation of one heat exchange fluid from another heatexchange fluid multilayered plastic tubes wherein at least one of thelayers is at least 50% by weight of polyamide resin and at least one ofthe layers is at least 50% by weight thermotropic liquid crystal polymer(LCP) blended with other polymer to make it tough enough so that in theform of 1.5 mm outside-diameter tube it can be bent around a radius of12.5 mm without cracking or delaminating. Preferably, the tubing canwithstand an internal pressure of 10,300 kPascals without bursting. Inpreferred embodiments, the LCP is toughened by blending with a usefulamount of rubber or other low-crystallinity polymer in amounts of about2 to about 30 percent by weight of the total weight of the LCP andrubber or other polymer, preferably about 5 to about 20 percent byweight. Preferably the rubber or other polymer has on it reactivefunctional groups such as epoxide groups.

[0018] A preferred embodiment of the heat exchanger of the inventionprovides a configuration made possible by the use of the materialsdescribed herein, with a set of at least three plastic tubes positionedaround a surface having the shape of a closed curve and on amultiplicity of spaced-apart spacers which hold said tubes in a spatialrelation to each other, said spacers providing a generally planar base,to form a layer of tubes, said base being generally perpendicular tosaid surface, wherein the set of tubes is positioned on said base in agenerally planar relation to form a layer, with a first tube in saidlayer having an inward side adjacent said surface and an outward sideopposite the inward side, a second tube in said layer proximate thefirst tube and on the outward side of said first tube opposite saidsurface, and each succeeding tube on the spacers with an inward sideproximate the outward side of previous tube, with a first end of each ofsaid tubes projecting off the base so that they can be joined togetherin a first header,

[0019] where the layer of tubes is about to reach the part of said tubesthat projects off of said base, the elevation of the set of tubes risesrelative to the base so the next layer of tubes lies on the first layerof tubes with the first tube adjacent said surface, with a multiplicityof layers, each overlaying the previous layer to form a group of layers,the second end of each tube projecting away from said group, and thefirst end of said tubes joined together to form said first header andsaid second end of said tubes joined together to form a second header.

[0020] Alternative embodiments provide for the spacers in succeedinglayers being held together by columns at the inner ends of each spacerin a layer and preferably additional columns also hold together theouter ends of each spacer. Alternatively, instead of using one or bothcolumns, a spacer could be attached to the one below it between thetubes in a layer, such as by snap-on connections.

[0021] In various embodiments, the surface is rounded or generallycircular or has a curvilinear shape other than rounded, such as a shapegenerally in the nature of a figure eight.

[0022] Preferably at least three spaced-apart spacers are provided ontop of each layer, configured so as to provide spacing both betweentubes in a layer and between layers, with the spacing within a layergenerally being less than the spacing between layers.

[0023] In further preferred embodiments, the steps are repeated to forma multiplicity of tube groups, each with its own terminations, each rowhas from 3 to 100 tubes, preferably from 15 to 30 tubes, more preferablyabout 20 tubes, each tube group has from 4 to 10 layers of tubes, andthe number of tube groups provided is from 3 to 10.

[0024] The heat exchanger can be a refrigeration heat exchanger, such asa condenser or an evaporator.

[0025] Also, as a process for preparing such plastic tube heatexchangers, the invention provides a method of making a plastic heatexchanger involving winding a set of at least three plastic tubes in ahelical manner around a surface having the shape of a closed curvedefining an aperture, with said tubes on a multiplicity of spaced-apartspacers which hold said tubes in a spatial relation to each other, saidspacers providing a generally planar base, to form a layer of tubes,said base being generally perpendicular to said surface, wherein the setof tubes is positioned on said base in a generally planar relation toform a layer, with a first tube in said layer having an inward sideadjacent said surface and an outward side opposite the inward side, asecond tube in said layer proximate the first tube and on the outwardside of said first tube opposite said surface, and each succeeding tubeon the spacers with an inward side proximate the outward side ofprevious tube, with a first end of each of said tubes projecting off thebase so that they can be joined together in a first header, and with thesteps of:

[0026] arranging said tubes in the described configuration,

[0027] positioning said tubes relative to each other so that the layerof tubes winds around the surface,

[0028] when the layer of tubes is about to reach the part of said tubesthat projects off of said base, adjusting the elevation of the set oftubes relative to the base if needed so the next layer of tubes lies onthe first layer of tubes with the first tube adjacent said surface,

[0029] repeating the previous step so that a group of layers having amultiplicity of layers is formed, each overlaying the previous layer,

[0030] providing a termination of said set of tubes to provide a secondend of each tube, and

[0031] joining together the first end of said tubes to form said firstheader and joining together said second end of said tubes in a secondheader.

[0032] Preferably the surface is round or has a curvilinear shape otherthan round, such as a shape generally in the nature of a figure eight.

[0033] Additional preferred methods provide the apparatus of theinvention, described above.

[0034] Preferably the plastic of the tubes is thermoplastic, at leastwhen it is being formed into the configuration of the heat exchanger.Normally it would not be crosslinked after forming, but in somecircumstances it may be desirable to do so.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention provides heat exchangers having plasticcoils constructed from materials which permit the construction ofcomplex geometries wherein the preferred geometry of the coil would bedifficult to produce from existing metal tube and fin constructions. Itfurther provides for specific coils and methods of manufacture of thesecoils which take advantage of the properties of these materials. In apreferred embodiment air-flow is through the sidewalls of the coilrather than through the faces. One advantage of this geometry is thatthere is no longer any wasted space in the center, as the fan is now inthe center.

[0036] According to the present invention, instead of winding tubelayers concentrically, they are wound helically, like a spring or spiralstaircase, starting on a flat plate or ring. The tubes are wound in aloop and when they reach the starting point, they are elevated to thenext layer, to begin another revolution, and so on, building a higherand higher stack of tubing. A commercial winding operation could involvebuilding a stack on a rotating disk. Spacers are inserted between eachlayer at several locations around the circumference (generally at 4 to12 locations) and provide the necessary spacing between tube layers.

[0037] This design offers the further advantage that multiple circuitscan be added more easily than with the concentric method of winding.Additional circuits can be added, one circuit at a time, to make thestack as high as needed. This method is expected to make it easier towind multiple parallel circuits, thus facilitating the development oflarger prototypes and scale-up to commercial manufacturing operations.

[0038] The combination of having the fan inside the coil, the use ofstackable spacers to hold the tubes in place, and the use of thisconfiguration, in which the coil is wound in a helical fashion, canprovide polymeric tubing exchangers which are compact, efficient andrelatively easy to construct.

[0039] Another potential feature is that the shape does not need to becircular, but can be, for instance, in a figure eight or racetrack shapeor in other desired shapes. It appears that the new method offers muchgreater flexibility in design.

[0040] A feature of some of the configurations of the invention may bethat the tubes near the outer perimeter are longer than the inner tubes.This will mean the flow of refrigerant will be higher in the inner tubesthan in the outer tubes in order to equalize the pressure drop. It ispossible to equalize the tubing length by flipping over the tube arrayafter half of the turns are completed, so that inside tubes then becomeoutside tubes.

[0041] Although this difference in tube length could sometimes be adisadvantage, it may also be an advantage in some applications whenunderstood. For example, if warm air is flowing through an evaporatorcoil from inside to outside, then it will have the greatest temperaturedifference when it hits the inside tubes, so the inner tubes may be ableto make good use of the higher refrigerant flow, thereby improvingoverall performance.

[0042] In order to make functional refrigerant-to-air heat exchangers,some means of joining the plastic tubes and connecting them to thecopper piping is desirable. This can achieved by sealing the gangedtubes into a copper pipe using a suitable epoxy resin available fromLoctite or Ciba-Geigy, such as Loctite E90FL toughened epoxy resin, atwo part product with an amine hardener; the copper pipe can then bejoined to the expansion or compression device by conventional metaljoining processes. Any number of tubes may be brought together in thismanner, depending on the dimensions of the tubes and the number of tubesrequired to effect heat transfer with minimal pressure drop.

[0043] The outer (surface) layer of the tubing may be the same as thebulk of the tube, preferably a polyamide, or may be a polyamide modifiedto improve bonding, coextruded on to the main structural layer ofpolyamide. Additional layers of thermoplastic can be incorporated intothe tubing such as by coextrusion, including a layer of thermotropicliquid crystal polymer (LCP) to enhance the barrier of the structure.Barrier layers could also be formed in other ways from other materials.The tubing structure may also contain layers of other materials,including inorganics, which may include coatings applied by variousmethods, to improve barrier properties.

[0044] The tubes can be of any diameter and wall thickness, consistentwith the need to separate inner and outer heat transfer fluids and totransfer heat. Typical wall thicknesses are 0.005-0.015 in. (0.13-0.38mm). In general, a minimum inner diameter of 0.030-0.060″ (0.76-1.5 mm)is desirable to avoid pluggage in use. The outer diameter is determinedby the internal pressure needs of the tube, generally up to a maximum of0.150-0.250 in. (3.8-6.4 mm).

[0045] For practical sizes and configurations of refrigerant heatexchangers, it is desirable to use tubes which are quite flexible andable to bend to a defined small radius without fracture or delamination,yet which also provide good barrier properties to keep in containedrefrigerant and to keep out air and moisture. Also, tubes which can bemelt-bonded to the spacers after forming the heat exchangers can bedesirable. The spacers can be made of a variety of materials, includingnylon 6 or 66, or of the same or similar materials as the tubes.

[0046] Other optional ingredients may be selected from flame retardants,anti-blocking agents, slip additives, pigments or dyes, processing aids,plasticizers and ultra-violet blocking agents. These may be used insuitable quantities as are well known to those skilled in the art.

[0047] Liquid crystal polymers are preferably used in forming layers inthe tubes, including as one of the materials an isotropic thermoplastic(ITP). It has been found that a layer of a thermotropic liquidcrystalline polymer (LCP) used in the heat exchange surface material(HESM) often alleviates or eliminates a variety of potential problems.By an LCP is meant a polymer that is anisotropic when tested in the TOTTest described in U.S. Pat. No. 4,118,372. An HESM is a material whichis used as part of a heat exchanger or a component thereof, and which isthe material through which the major portion of the heat that isexchanged between the two fluids (gas or liquid) is meant to flow. Italso performs the function of keeping apart the two fluids between whichheat is being exchanged. Isotropic herein means that the polymer isisotropic when tested by the TOT Test described in U.S. Pat. No.4,118,372, which is hereby included by reference. Any ITP may be used solong as it meets certain requirements. It must of course withstand thetemperatures to which the HESM is exposed, and should throughout thattemperature range provide sufficient strength (together with the LCP) tothe HESM to reasonably maintain its shape and contain the fluids in theheat exchanger, as needed. If it is exposed to one or more of the fluidsin the heat exchanger (or any other adventitious materials that maycontact it) it should be preferably reasonably chemically stable tothose fluids so as to maintain its integrity.

[0048] Although various types of heat exchangers made simply of ITPshave been described, ITPs sometimes have serious drawbacks when the arethe only materials in HESMS. Sometimes an ITP may not be chemicallystable to one or more of the fluids in the heat exchanger, for instance,many polyesters hydrolyze or otherwise degrade in the presence of water,water-alcohol, or water-glycol mixtures, especially at higher thanambient temperatures. Many ITPs are relatively permeable to many liquidsand/or gases, and therefore allow losses and/or migration of thesematerials in or from the heat exchanger. Some ITPs may be swollen by oneor more of the fluids used in the heat exchanger thereby changing theirdimensions and/or physical properties. All of the above are of courseproblems in plastic heat exchangers.

[0049] If the LCP layer is placed between a fluid and any particular ITPin the HESM it usually protects that ITP from chemical degradation bythe fluid, and/or also often protects the ITP from being swollen by thatfluid. In addition, even if the ITP is swollen, the LCP because of itshigh relative stiffness, and the fact that it is not swollen by manyfluids, help the overall HESM maintain its shape and dimensions. Also,the LCP acts as an excellent barrier layer to many fluids. For instance,in automotive heat exchangers which help cool the engine, the commonlyused internal coolant is a mixture of a glycol and water, and theexternal coolant is air. With many ITPs diffusion of water and/or glycolis so rapid that frequent replenishment of the water/glycol mixture isneeded. If an LCP layer is included, the diffusion is greatly decreased.

[0050] In order to obtain rapid heat transfer through the HESM,thickness through the material between the heat transfer fluids shouldbe a small as possible. This would be true with any material used for anHESM, but is especially important with plastics since their heattransfer coefficients are usually relatively low when compared tometals. Since the LCP is usually the more expensive of the polymerspresent in the HESM, it is economically preferable to limit its use.Therefore, in most constructions it is preferred that the LCP is presentin relatively thin layer(s) and that layer(s) of the ITP be relativelythick so as to carry much of the structural load of the HESM (i.e.,pressure of the fluid(s), maintain structural shape and dimensions,etc.).

[0051] The HESM is made up of one or more LCP layers and one or morelayers of ITP. If more than one layer of LCP or ITP is present, morethan one type of LCP or ITP, respectively, can be used. In additionother layers may be present. For example, so called tie layers, alsocalled adhesive layers, may be used to increase the adhesion betweenvarious LCP and ITP layers, or between ITP layers or between LCP layers.The number and placement of the various layers in the HESM will varydepending on the particular polymers chosen, the fluids used in or bythe heat exchanger, temperature requirements, environmental needs, etc.

[0052] Most commonly, tie layers and LCP layers will be relatively thincompared to the ITP layer(s). Typical constructions are given below,wherein Fluids 1 and 2 represent the fluids involved in the heattransfer:

[0053] (a) Fluid 1/LCP/ITP/Fluid 2

[0054] (b) Fluid 1/ITP-1/LCP/ITP-2/Fluid 2

[0055] (c) Fluid 1/LCP-1/ITP/LCP-2/Fluid 2

[0056] (d) Fluid 1/ITP-1/LCP-1/ITP-2/LCP-2/Fluid 2

[0057] (e) Fluid 1/ITP-1/ITP-2/LCP/Fluid 2

[0058] (f) Fluid 1/LCP-1/ITP-1/ITP-2/LCP-2/Fluid 2

[0059] In all of the above constructions, tie layers may be presentbetween all, some or none of the various polymer layers.

[0060] Some of the above constructions may be particularly useful incertain situations. If Fluid 1 but not Fluid 2 chemically attacked theITP, construction (a) may be particularly useful, but (c) and (f) mayalso be utilized. If both Fluids 1 and 2 attacked the ITP presentconstruction (c) or (f) may be particularly useful. If one wanted tominimize diffusion of one fluid to another, a construction having twoLCP layers, such as (c), (d) or (f) could be chosen. If a specialsurface is required to reduce abrasive damage on the Fluid 1 side, butgreat stiffness is also required from the ITP, a construction such as(e) could be chosen wherein ITP-1 and ITP-2 have the requisiteproperties. These and other combinations of layers having the correctproperties for various applications will be obvious to the artisan.

[0061] Useful LCPs include those described in U.S. Pat. Nos. 3,991,013,3,991,014 4,011,199, 4,048,148, 4,075,262, 4,083,829, 4,118,372,4,122,070, 4,130,545, 4,153,779, 4,159,365, 4,161,470, 4,169,933,4,184,996, 4,189,549, 4,219,461, 4,232,143, 4,232,144, 4,245,082,4,256,624, 4,269,965, 4,272,625, 4,370,466, 4,383,105, 4,447,592,4,522,974, 4,617,369, 4,664,972, 4,684,712, 4,727,129, 4,727,131,4,728,714, 4,749,769, 4,762,907, 4,778,927, 4,816,555, 4,849,499,4,851,496, 4,851,497, 4,857,626, 4,864,013, 4,868,278, 4,882,410,4,923,947, 4,999,416, 5,015,721, 5,015,722, 5,025,082, 5,086,158,5,102,935, 5,110,896, and 5,143,956, and European Patent Application356,226. Useful thermotropic LCPs include polyesters,poly(ester-amides), poly(ester-imides), and polyazomethines. Especiallyuseful are LCPs that are polyesters or poly(ester-amides). It is alsopreferred in these polyesters or poly(ester-amides) that at least about50 percent, more preferably at least about 75 percent, of the bonds toester or amide groups, i.e., the free bonds of —C(O)O— and —C(O)NR¹—wherein R¹ is hydrogen or hydrocarbyl, be to carbon atoms which are partof aromatic rings. Included within the definition herein of an LCP is ablend of 2 or more LCPs or a blend of an LCP with one or more ITPswherein the LCP is the continuous phase.

[0062] Useful ITPs are those that have the requisite properties asdescribed above, and include: polyolefins such as polyethylene andpolypropylene; polyesters such as poly(ethylene terephthalate,poly(butylene terephthalate), poly(ethylene 2,6-napthalate), and apolyester from 2,2-bis(4-hydroxyphenyl)propane and a combination ofisophthalic and terephthalic acids; styrenics such as polystyrene andcopolymers of styrene with (meth)acrylic esters;acrylonitrile-butadiene-styrene thermoplastics; (meth)acrylic polymersincluding homo- and copolymers of the parent acids, and/or their estersand/or amides; polyacetals such as polymethylene oxide; fully andpartially fluoropolymers such as polytetrafluoroethylene,polychlorotrifluoroethylene,poly(tetrafluoroethylene/hexafluoropropylene) copolymers,poly[tetrafluoroethylene/perfluoro(propyl vinyl ether)] copolymers,poly(vinyl fluoride), poly(vinylidene fluoride), and poly(vinylfluoride/ethylene) copolymers; ionomers such as an ionomer of anethylene-acrylic acid copolymer; polycarbonates; poly(amide-imides);poly(ester-carbonates); poly(imide-ethers); polymethylpentene; linearpolyolefins such as polypropylene; poly(etherketoneketone); polyimides;poly(phenylene sulfide); polymers of cyclic olefins; poly(vinylidenechloride); polysulfones; poly(ether-sulfones); and polyamides such asnylon-6,6 nylon-6, nylon-6,12, nylon-6,12, nylon 4,6, and the polyamidesfrom terephthalic acid and/or isophthalic acid and 1,6-hexanediamineand/or 2-methyl-1,5-pentanediamine. Polyamides are preferred ITPs andpreferred amides are nylon-6,6, nylon-6, and a copolymer of terephthalicacid with 1,6-hexandiamine and 2-methyl-1,5-pentanediamine wherein1,6-hexanediamine is about 30 to about 70 mole percent of the totaldiamine used to prepare the polymer. Especially preferred polyamides arenylon-6,6, nylon-6 and a copolymer of terephthalic acid with1,6-hexandiamine and 2-methyl-1,5-pentanediamine wherein1,6-hexanediamine is about 50 mole percent of the total diamine used toprepare the polymer. Included within the definition of ITP herein areblends of 2 or more ITPs or blends of one or more ITPs with an LCPprovided that the ITP(s) is the continuous phase.

[0063] One or more of the LCPs and ITPs may be toughened. Toughening isknown in the art, and may be accomplished by adding one or more or arubber, functionalized rubber, resin which reacts with the LCP or ITPsuch as an epoxy resin, or other materials. Toughened polyamides arepreferred.

[0064] The polymers may contain other materials conventionally found inpolymers, such as fillers, reinforcing agents, antioxidants,antiozonants, dyes, pigments, etc. An especially useful material is afiller with high heat conductivity, which may increase the efficiency ofthe heat exchanger.

[0065] Between the layers of tubing made by coextrrusion, tie layers canbe used to minimize the likelihood of delamination. The composition of atie layer will depend on which two polymers are on either side of it.For instance the tie layer may be an ITP functionalized or grafted toprovide adhesion between the ITP and LCP layers, or may be a blend ofone or more ITPs and one or more LCPs.

[0066] Preferably LCP used in the invention will be toughened,especially if it is to be used in tubes which will be wound to a fairlytight radius, such as down to 12.5 mm. Such a small radius may be foundeither in the coils themselves, such as in a condenser without a fan inthe center, or it may be found in a transition form the coil to theoutside connection. LCPs can be toughened as is known in the art invarious ways, for example by melt blending an LCP with a rubber or otherpolymer having low crystallinity. In the melt blending it is preferredthat the rubber or other polymer be dispersed into the LCP so that theLCP is the continuous phase and rubber or other polymer is present inrelatively small particles. It is often preferred that the rubber orother polymer have reactive functional groups on it such as epoxidegroups. It is known that this often improves the toughening of the LCPand also may improve the adhesion of the LCP layer to other polymerlayers in the tubing. When toughening an LCP a useful amount of rubberor other polymer is about 2 to about 30 percent by weight of the totalweight of the LCP and rubber or other polymer, preferably about 5 toabout 20 percent by weight. Relevant teachings may be found in U.S. Pat.No. 5,997,765—Furuta and Yamaguchi (1999), EP Appl. 0 380 112 A2—Izumiet al. (1990) and PCT Publication WO 93/24574—Heino et al. (1993) whichare all hereby included by reference.

[0067] Typical thicknesses for ITP layers will range from about 0.025 toabout 0.25 mm. Typical thicknesses for LCP layers will be about 0.01 toabout 0.1 mm. Tie layers will usually be as thin as possible, consistentwith their providing adhesion between polymer layers. This is usuallyabout 0.01 to about 0.1 mm. The total thickness of the structure ispreferably less than about 0.7 mm, more preferably about 0.12 to about0.5 mm, and especially preferably about 0.15 mm to about 0.4 mm.

[0068] With reference to the drawings, FIG. 1 illustrates the beginningof a process of making a plastic heat exchanger of the invention. A setof tubes 10 is laid on spacers 29A (-C) on a base plate 11. A first endof tubes 21, 22, 23, 24, 25 and 26 extend out from base 10 where theycan be gathered together in a header 20, such as a copper tube. Thesecond end of tubes 21-26 can be fed through a guide 30 from drums31-36, respectively. Base 11 is provided with additional spacers, 29 Band C. Preferably the spacers are attached to a column 27A at theirinner ends, and preferably they are also attached to another column 28A(-C) at their outer ends, to hold them in place. In the drawings, theheat exchangers illustrated are in a cylindrical shape, being formedaround a surface 12 incorporating an aperture 13. However, it will beapparent that heat exchangers of the invention can be formed in othercurvilinear shapes, depending on where the columns are situated on thebase. Also, surface 12 can extend above the plane of base 11 in the formof a mandrel or other form, or it can simply be a surface shaped inspace without any physical embodiment. If a mandrel is used, it can beremoved after forming the heat exchanger, or it could be made of aporous material, such as a mesh or a perforated sheet, so that coolantcan flow through it. Removal of a mandrel could be done physically orchemically, by etching it away. Furthermore, the tubes can be laid downon the spacers by hand or with whatever degree of automation is desired,with reels 31-36 supplying the tubes, or even with the tubes previouslycut to the desired lengths and fed in by hand.

[0069] FIG. 2 illustrates a further step in the process of theinvention, with the set of tubes 21-26 having been wound around surface13 and columns 27 A and B, then rising above the first layer of tubes at40 to overlay the first layer in forming the second layer.

[0070] Outer columns 28 A-C are not shown in FIG. 2 to indicate thatthey are optional.

[0071] FIG. 3 shows a plastic tube heat exchanger of the invention afterthe winding of tubes has been completed and headers 44 and 45 have beenput in place on the bundles of tubes 46 and 47 coming away from theexchanger. At the center of the exchanger is a fan 41, to draw air orother gas in from the ends and cause it to flow out through the sides,as shown at 42. Spacers 29 and columns 27 and 28 are indicated, holdingapart the tubes which can be 20 or more, or less, in each layer.

[0072] FIG. 4 shows an elevation of the heat exchanger of FIG. 3,illustrating tubes at 10, base 11, spacers 43, bundles of tubes 46, andheaders 44. The spacers shown could be for inlet or outlet of coolantwhich will flow through the tubes.

[0073] FIG. 5 shows a spacer 29 with grooves 51 and 52 on its top andbottom, respectively, for holding tubes apart.

[0074] FIG. 6 is a side view of the spacer, also showing holes 53 and 54for fitting on the columns.

[0075] The selection of polymeric tubing for heat exchangers containingrefrigerants must satisfy certain criteria:

[0076] a) it must withstand internal pressures appropriate tocontainment of refrigerants, including normal operating pressures, testpressures, and safety mandated overpressure capabilities

[0077] b) it must prevent or minimize egress of refrigerant and ingressof air or water

[0078] c) it must be amenable to coiling tightly without kinking orfracturing the LCP layer

[0079] d) the walls of the tubing must be thin enough so as not tosubstantially impede heat transfer

[0080] These properties are affected by the tubing diameter, thethicknesses of individual layers, and the modification of the LCP withITP.

EXAMPLE

[0081] As an example, the tube structure used to construct arefrigeration evaporator was as follows; Outer diameter 0.059 inch (1.5mm) Inner Layer—3 mils (76 micron) of a compounded blend of the LCP ofexample 6 of U.S. Pat. No. 5,525,700—Samuels and Waggoner (1996) (90%w/w), ethylene butylacrylate (5% w/w)(such as is available from Chevronas grade 1802 (18% BA) and Elvaloy 3934-4 (5% w/w)(ethylene/butylacrylate/ glycidyl methacrylate copolymer). The LCP is a copolymer ofbiphenol, hydroquinone, terephthalic acid, 2,6-naphthalenedicarboxylicacid, p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid in a molarratio of 50/50/70/30/270/50). Middle Layer—1 mil (25microns) of Bynel4206 (LDPE grafted with maleic anhydride) Outer Layer—5 mil (127microns) of Zytel 42A NC010 (nylon 6,6), containing minor additivesincluding carbon black pigment, heat stabilizer and lubricant. Elvaloy,Bynel and Zytel are trademarks of DuPont Company, from whom the productsare available.

[0082] The tubing of this example has a burst pressure in excess of 1500psig (10,300 kpascals) and can be coiled to a radius of curvature of 0.5inches (12.3 mm)without kinking (all at 50% RH) and is thereforesuitable for constructing coiled heat exchangers to handle refrigerantssuch as chlorodifluoromethane.”

What is claimed is:
 1. A plastic tube heat exchanger utilizing forseparation of one heat exchange fluid from another heat exchange fluidmultilayered plastic tubes wherein at least one of the layers is atleast 50% by weight of polyamide resin and at least one of the layers isat least 50% by weight thermotropic liquid crystal polymer blended withother polymer to make it tough enough so that in the form of 1.5 mmoutside-diameter tube it can be bent around a radius of 12.5 mm withoutcracking or delaminating.
 2. The heat exchanger of claim 1 wherein thetubing can withstand an internal pressure of 10,300 kPascals withoutbursting.
 3. The heat exchanger of claim 1 wherein the liquid crystalpolymer is toughened by melt blending with small particles of rubber orother low-crystallinity polymer about 2 to about 30 percent by weight ofthe total weight of the liquid crystal polymer and rubber or otherpolymer rubber or other polymer having low crystallinity having reactivefunctional groups.
 4. A plastic tube heat exchanger having a set of atleast three plastic tubes positioned around a surface having the shapeof a closed curve and on a multiplicity of spaced-apart spacers whichhold said tubes in a spatial relation to each other, said spacersproviding a generally planar base, to form a layer of tubes, said basebeing generally perpendicular to said surface, wherein the set of tubesis positioned on said base in a generally planar relation to form alayer, with a first tube in said layer having an inward side adjacentsaid surface and an outward side opposite the inward side, a second tubein said layer proximate the first tube and on the outward side of saidfirst tube opposite said surface, and each succeeding tube on thespacers with an inward side proximate the outward side of previous tube,with a first end of each of said tubes projecting off the base so thatthey can be joined together in a first header, where the layer of tubesis about to reach the part of said tubes that projects off of said base,the elevation of the set of tubes relative to the plate rises relativeto the base so the next layer of tubes lies on the first layer of tubeswith the first tube adjacent said surface, with a multiplicity oflayers, each overlaying the previous layer to form a group of layers,the second end of each tube projecting away from said group, and thefirst end of said tubes joined together to form said first header andsaid second end of said tubes joined together to form a second header.5. The plastic tube heat exchanger of claim 4 wherein the spacers insucceeding layers are held together by columns at the inner ends of eachspacer in a layer.
 6. The plastic tube heat exchanger of claim 4 whereincolumns also hold together the outer ends of each spacer.
 7. The plastictube heat exchanger of claim 4 wherein said surface is generallycircular.
 8. The plastic tube heat exchanger of claim 4 wherein saidsurface has a curvilinear shape other than generally circular.
 9. Theplastic tube heat exchanger of claim 5 wherein said surface has a shapegenerally in the nature of a figure eight.
 10. The plastic tube heatexchanger of claim 4 wherein a multiplicity of spaced-apart spacers areprovided on top of each layer, configured so as to provide spacing bothbetween tubes in a layer and between layers.
 11. The plastic tube heatexchanger of claim 11 wherein at least three spacers are provided oneach layer.
 12. The plastic tube heat exchanger of claim 11 wherein thespacing within a layer is less than the spacing between layers.
 13. Theplastic tube heat exchanger of claim 4 wherein there are a multiplicityof tube groups, each with its own terminations.
 14. The plastic tubeheat exchanger of claim 4 wherein each row has from 3 to 100 tubes. 15.The plastic tube heat exchanger of claim 12 wherein each row has 15 to30 tubes.
 16. The plastic tube heat exchanger of claim 4 wherein eachtube group has from 4 to 10 layers of tubes.
 17. The plastic tube heatexchanger of claim 13 wherein the number of tube groups provided is from3 to
 10. 18. A plastic tube heat exchanger of claim 4 which is arefrigerant heat exchanger.
 19. A condenser heat exchanger of claim 18.20. An evaporator heat exchanger of claim
 18. 21. A method of making aplastic tube heat exchanger of claim 4 involving winding a set of atleast three thermoplastic tubes in a helical manner around a surfacehaving the shape of a closed curve defining an aperture, with said tubeson a multiplicity of spaced-apart spacers which hold said tubes in aspatial relation to each other, said spacers providing a generallyplanar base, to form a layer of tubes, said base being generallyperpendicular to said surface, wherein the set of tubes is positioned onsaid base in a generally planar relation to form a layer, with a firsttube in said layer having an inward side adjacent said surface and anoutward side opposite the inward side, a second tube in said layerproximate the first tube and on the outward side of said first tubeopposite said surface, and each succeeding tube on the spacers with aninward side proximate the outward side of previous tube, with a firstend of each of said tubes projecting off the base so that they can bejoined together in a first header, and with the steps of: arranging saidtubes in the described configuration, positioning said tubes relative toeach other so that the layer of tubes winds around the surface, when thelayer of tubes is about to reach the part of said tubes that projectsoff of said base, adjusting the elevation of the set of tubes relativeto the plate if needed so the next layer of tubes lies on the firstlayer of tubes with the first tube adjacent said surface, repeating theprevious step so that a tube group having a multiplicity of layers isformed, each overlaying the previous layer, providing a termination ofsaid set of tubes to provide a second end of each tube, and joiningtogether the first end of said tubes to form said first header andjoining together said second end of said tubes in a second header. 22.The method of claim 21 wherein said surface is generally circular. 23.The method of claim 21 wherein said surface has a curvilinear shapeother than generally circular.
 24. The method of claim 23 wherein saidsurface has a shape generally in the nature of a figure eight.
 25. Themethod of claim 21 wherein a multiplicity of spaced-apart spacers areprovided on top of each layer, configured so as to provide spacing bothbetween tubes in a layer and between layers.
 26. The method of claim 25wherein at least three spacers are provided on each layer.
 27. Themethod of claim 26 wherein the spacing between tubes within a layer isless than the spacing between layers.
 28. The method of claim 21 whereinthe steps are repeated to form a multiplicity of tube groups, each withits own terminations.
 29. The method of claim 21 wherein each row hasfrom 3 to 100 tubes.
 30. The method of claim 27 wherein each row has 15to 20 tubes.
 31. The method of claim 21 wherein each tube group has from4 to 10 layers of tubes.
 32. The method of claim 28 wherein the numberof tube groups provided is from 3 to 10.